Components of various industrial devices are often subjected to extreme conditions, such as high impact contact with abrasive surfaces. For example, such extreme conditions are commonly encountered during subterranean drilling for oil extraction or mining purposes. Diamond, with its unsurpassed wear resistance, is the most effective material for earth drilling and similar activities that subject components to extreme conditions. Diamond is exceptionally hard, conducts heat away from the point of contact with the abrasive surface, and may provide other benefits in such conditions.
Diamond in its polycrystalline form has added toughness as compared to single crystal diamond due to the random distribution of the diamond crystals, which avoids the particular planes of cleavage found in single diamond crystals. Therefore, polycrystalline diamond is frequently the preferred form of diamond in many drilling applications or other extreme conditions. Device elements have a longer usable life in these conditions if their surface layer is made of diamond, typically in the form of a polycrystalline diamond (PCD) compact, or another super abrasive material.
Elements for use in harsh conditions may contain a PCD layer bonded to a substrate. The manufacturing process for a traditional PCD is very exacting and expensive. The process is referred to as “growing” polycrystalline diamond directly onto a carbide substrate to form a polycrystalline diamond composite compact. The process involves placing a cemented carbide piece and diamond grains mixed with a catalyst binder into a container of a press and subjecting it to a press cycle using ultrahigh pressure and temperature conditions. The ultrahigh temperature and pressure are required for the small diamond grains to form into an integral polycrystalline diamond body. The resulting polycrystalline diamond body is also intimately bonded to the carbide piece, resulting in a composite compact in the form of a layer of polycrystalline diamond intimately bonded to a carbide substrate.
A problem with PCD arises from the use of cobalt or other metal catalyst/binder systems to facilitate polycrystalline diamond growth. After crystalline growth is complete, the catalyst/binder remains within pores of the polycrystalline diamond body. Because cobalt or other metal catalyst/binders have a higher coefficient of thermal expansion than diamond, when the composite compact is heated, e.g., during the brazing process by which the carbide portion is attached to another material, or during actual use, the metal catalyst/binder expands at a higher rate than the diamond. As a result, when the PCD is subjected to temperatures above a critical level, the expanding catalyst/binder causes fractures throughout the polycrystalline diamond structure. These fractures weaken the PCD and can ultimately lead to damage to or failure.
As a result of these or other effects, it common to remove the catalyst from part of the PCD layer, particularly the parts near the working surface. The most common process for catalyst removal uses a strong acid bath, although other processes that employ alternative acids or electrolytic and liquid metal techniques also exist. In general, removal of the catalyst from the PCD layer using an acid-based method is referred to as leaching. Acid-based leaching typically occurs first at the outer surface of the PCD layer and proceeds inward. Thus, traditional elements containing a leached PCD layer are often characterized as being leached to a certain depth from their surface. PCD, including regions of the PCD layer, from which a substantial portion of the catalyst has been leached is referred to as thermally stable PCD (TSP). Examples of current leaching methods are provided in U.S. Pat. No. 4,224,380; U.S. Pat. No. 7,712,553; U.S. Pat. No. 6,544,308; U.S. 20060060392 and related patents or applications.
Acid-leaching leaching must also be controlled to avoid contact between substrate or the interface between the substrate and the diamond layer and the acids used for leaching. Acids sufficient to leach polycrystalline diamond severely degrade the much less resistant substrate. Damage to the substrate undermines the physical integrity of the PCD element and may cause it to crack, fall apart, or suffer other physical failure while in use, which may also cause other damage.
The need to carefully control leaching of elements containing a PCD layer significantly adds to the complications, time, and expense of PCD manufacturing. Additionally, leaching is typically performed on batches of PCD elements. Testing to ensure proper leaching is destructive and must be performed on a representative element from each batch. This requirement for destructive testing further adds to PCD element manufacturing costs.
Attempts have been made to avoid the problems of leaching a fully formed element by separately leaching a PCD layer, then attaching it to a substrate. However, these attempts have failed to produce usable elements. In particular, the methods of attaching the PCD layer to the substrate have failed during actual use, allowing the PCD layer to slip or detach. In particular, elements produced using brazing methods, such as those described in U.S. Pat. No. 4,850,523; U.S. Pat. No. 7,487,849, and related patents or applications, or mechanical locking methods such as those described in U.S. Pat. No. 7,533,740 or U.S. Pat. No. 4,629,373 and related patents or applications are prone to failure.
Other methods of bonding a PCD layer to a pre-formed substrate are described in U.S. Pat. No. 7,845,438, but require melting of a material already present in the substrate and infiltration of the PCD layer by the material.
In still other methods, leached PCD layers have been attached directly to the gage region of a bit by infiltrating the entire bit and at least a portion of the PCD layer with a binder material. Although these methods are suitable to attaching PCD to a gage region, where it need not be removed during the lifetime of the bit, they are not suitable for placing PCD layers in the cutting regions of a bit, where replacement or rotation of the PCD is desirable for providing normal bit life.
Using still other methods, PCD elements, often referred to as geosets, have been incorporated into the exterior portions of drill bits. Geosets are typically coated with a metal, such as nickel (Ni). Geoset coatings may provide various benefits, such as protection of the diamond at higher temperature and improved bonding to the drill bit matrix.
Accordingly, a need exists for an element, including a rotatable or replaceable element, having a leached PCD layer, such as a TSP body, attached to a base or substrate sufficiently well to allow use of the element in high temperature conditions such as those encountered by cutting elements of an earth-boring drill bit.